Conventional systems for transporting passengers/goods, such as moving walkways or escalators, include a chain of conveyor pallets or steps which move in a circuit for the purpose of providing continuous movement along a specific path. The conveyor pallets or steps are connected to said chain circuit, which moves as a result of a drive system. The drive system usually consists of a chain of conveyor plates, gear wheels, a shaft and an electric geared motor provided with an emergency brake. The electric motor drives the shaft to which the gear wheels are integrally attached, which gear wheels transmit the movement to the links of the chain of conveyor pallets or steps. The conveyor pallets or steps move in the same way as said chain does. The drive system is located at only one of the ends of the moving walkway or escalator while the elements responsible for providing the tensing of the system are usually located at the opposite end. The conveyor pallets or steps travelling along the bottom part of the moving walkway or escalator in its entirety following the return path turn over at these end areas of the moving walkway or escalator.
For assuring the system safety in the event of system failures and keeping the belt of pallets or steps immobile in the stopped state, even without current electric, it is necessary to provide the system with a braking system assuring this. Said braking system has to be in a braking situation even without electric voltage being applied.
It is also necessary for said braking system to be able to stop the movement of the belt of pallets or steps with the machine under any load state at a distance such that it assures the smallest braking distance which does not endanger passenger safety.
The braking system traditionally consists of brake shoes which are pushed by means of springs against the side of a drum or flywheel integrally attached to the shaft of the geared motor when braking. To open the brake and allow the normal operation of the machine one or several linear solenoids are arranged, acting in the direction opposite to the spring or springs, such that when they are energized they are able to move the shoes from the surface of the drum or flywheel, allowing the free rotation of the system.
Over the years different mechanical schemes have been proposed to improve the efficacy of this system, such as that described in patent EP0388299-B1 of Otis Elevator, for example, although its operating principle is similar to that described above.
All these spring-guided emergency braking systems require using a flywheel to enable maintaining safe braking distances given different load states of the system, particularly both in the case of an unloaded and a fully loaded machine in an upward direction in the case of an escalator.
It is further necessary to adjust the braking force by means of pre-loading the springs which “close” the shoes because the deceleration obtained depends on them. These adjustments will have to be repeated every so often because both the springs and the shoe friction elements experience wear affecting their braking ability.
All this has lead to the development of different braking systems which can obtain pre-programmed decelerations regardless of the weight of the passengers on the machine and the rotating direction at the time of braking in a safe manner.
One of the solutions used consists of providing a conventional brake, the shoes of which are forced by springs into the de-energized position of the coil (the coils have no electric power supply, i.e., without energy because their power supply has been interrupted by the system by means of a “short-circuiting” device such as a contactor or relay) with a control system which acts on the solenoids while braking such that these generate a force against the springs such that the braking torque is reduced for adapting it to the load state of the escalator or walkway at that time, achieving the required braking distance. The problem of this system is that in the event of a failure, the system brakes with all the braking force available, whereby it is not possible to comply with the braking distances required by law depending on the load state.
Other braking systems are based on using a variable frequency drive powering the motor to perform the braking ramp and thus achieve a controlled deceleration. The drawbacks of this solution include the increase in cost for having to use this variable frequency drive because it is an optional element not incorporated in all machines. It is also necessary to recalculate the power of this variable drive to enable handling the worst system load conditions, which results in an increase in cost and of the necessary space with respect to a solution in which the variable drive is not used while braking. Furthermore, the use of the variable drive does not eliminate the need to have a conventional emergency brake.